For Problems 2.6 and 2.7, calculate the uniform load (in addition to the beam weight) that will cause the sections to begin to crack if they are used for 2 8-ft 8-ft simple spans f’c=4000 psi, fr= 7.5(f’c)^0.5 and reinforced concrete weight = 150 lb/ft3. 2.6
b=14 in = 350 mm h=24 in = 600 mm p=150 lb/ft3 *(3.28^3)(9.81)/(2.204)= 23.553 KN/m3 L=28 ft = 8.54 m f’c=4000 psi=27.58 MPa≈ 28 MPa
For Problems 2.8 to 2.14, assume the sections have cracked and use transformed-area method to compute their flexural stresses for loads or moments given. 2.11
M=110 ft-k(1.35582 KN-m)=149.14 KN-m n=8 b=14 in= 355.6 mm h=24 in= 609.6 mm 18 in= 457.2 mm 3 in= 76.2 mm A#9 =645 mm2
El eje neutro se encuentra más arriba
2.16 Compute the resisting moment of the beam of Problem 2.13 if eight #10 bars are used and n=10 fs=20 000 psi and fc=1125 psi. Use the transformed area method.
